SCOS 02/2 Scientific Advice on Matters Related to the Management of Seal Populations: 2002 Contents SCOS 02/2 Scientific Advice SCOS 02/2 ANNEX I The Status of Grey and Common Seals in the North Atlantic Region SCOS 02/2 ANNEX II The Status of British Grey Seal Populations Appendix 1 Estimates of pup production SCOS 02/2 ANNEX III The Status of British Common Seal Populations SCOS 02/2 ANNEX IV Population dynamics of grey seals SCOS 02/2 ANNEX V Information papers provided for SCOS 1 SCOS 02/2 Scientific advice Background Under the Conservation of Seals Act 1970, the Natural Environment Research Council (NERC) has a duty to provide scientific advice to government on matters related to the management of seal populations. NERC has appointed a Special Committee on Seals (SCOS) to formulate this advice so that it may discharge this statutory duty. Terms of Reference for SCOS and its current membership are given at the end of this document. Formal advice is given annually based on the latest scientific information provided to SCOS by the Sea Mammal Research Unit (SMRU – a NERC Collaborative Centre at the University of St Andrews). SMRU also provides to government scientific review of applications for licences to shoot seals, and information and advice in response to parliamentary questions and correspondence. This report provides scientific advice on matters related to the management of seal populations for the year 2002. It begins with some general information on British seals, gives information on their current status, and addresses specific questions raised by the Scottish Executive Environment Rural Affairs Department (SEERAD). Appended to the main report are two annexes giving more detail about the status of the two species of seal around Britain: grey and common (harbour) seals. General information on British seals Grey seals The grey seal is the larger of the two species of seal that breed around the coast of the British Isles. It is found across the North Atlantic Ocean and in the Baltic Sea (Annex I, Table 1). There are two centres of population in the North Atlantic; one in the region of Nova Scotia and the Gulf of St Lawrence and the other around the coast of the UK and especially in Scottish coastal waters. The largest population is in Canada. Populations in all three centres are increasing, although numbers are still relatively low in the Baltic where the population went through a long-term decline possibly caused by reproductive failure due to pollution. Grey seals come ashore on remote islands and coastlines to give birth to their pups in the autumn, to moult in spring, and at other times of the year to haul out between trips to forage for food at sea. Female grey seals give birth to a single white-coated pup, which moults and is abandoned by its mother about 3 weeks later. About 38% of the world population of grey seals is found in Britain and over 90% of British grey seals breed in Scotland, the majority in the Hebrides and in Orkney (Annex I, Table 1). There are also breeding colonies in Shetland, on the north and east coasts of mainland Britain and in southwest Britain. Although the number of pups born at colonies in the Hebrides has remained approximately constant since 1992, the total number of pups born throughout Britain has grown steadily since the 1960s when records began. In 2001, there were an estimated 42,000 grey seal pups born in Britain. This equates to a total population of about 130,000 grey seals. Adult male grey seals may weigh up to 350 kg and grow to over 2.3 m in length. Females are smaller at a maximum of 250 kg in weight and 2 m in length. Grey seals are long-lived animals. Males will lives for over 20 years and begin to breed from about age 10. Females often live for over 30 years and begin to breed at about age 5. Grey seals feed mostly on fish that live on or close to the seabed. The diet is composed particularly of sandeels, whitefish (cod, haddock, whiting, ling), and flatfish (plaice, sole, flounder, dab) but varies seasonally and from region to region. Food requirements depend on the size of the seal and oiliness of the prey but an average figure is 7 kg of cod or 4 kg of sandeels per day. 2 SCOS 02/2 Common seals Common seals are found around the coasts of the North Atlantic and North Pacific from the subtropics to the Arctic. Common seals in Europe belong to a distinct sub-species which, in addition to the UK, is found mainly in Icelandic, Norwegian, Danish, German and Dutch waters. Britain holds approximately 40% of the world population of the European sub-species (Annex I, Table 2). Common seals are widespread around the west coast of Scotland and throughout the Hebrides and Northern Isles. On the east coast, their distribution is more restricted with particular concentrations in the Wash, Firth of Tay and the Moray Firth Between 1996 and 2001, 34,625 common seals were counted in the whole of Britain, of which 30,196 (87%) were in Scotland and 4,245 (13%) were in England. The total British population cannot be estimated accurately because it is not possible to count all individuals in the population. Accounting for those animals that are not seen during surveys using a conversion factor leads to an estimate for the total British population of approximately 50-60 thousand animals. The population along the east coast of England (mainly in The Wash) was severely affected by the phocine distemper virus (PDV) epidemic in 1988. Numbers in England have increased since then, but have only recently recovered to the pre-epidemic level. The new epidemic in 2002 is likely to have a similar impact to the one in 1988. Common seals come ashore in sheltered waters typically on sandbanks and in estuaries but also in rocky areas. They give birth to their pups in June and July and moult in August. At other times of the year, common seals haul out on land regularly in a pattern that is often related to the tidal cycle. Common seal pups are born without a white coat and can swim almost immediately. Adult common seals typically weigh about 80-100 kg. Males are slightly bigger than females. Like grey seals, common seals are long-lived with individuals living up to 20-30 years. Common seals normally feed within 40-50 km around haul out sites. They take a wide variety of prey including sandeels, whitefish, herring and sprat, flatfish, octopus and squid. Diet varies seasonally and from region to region. Because of their smaller size, common seals eat less food than grey seals, perhaps 3-5 kg per day depending on the prey species. 3 SCOS 02/2 Current status of British grey seal populations The number of pups born in a seal population can be used as an indicator of the size of the population. Each year, SMRU conducts aerial surveys of the major grey seal breeding colonies in Britain to determine the number of pups born (pup production). These sites include about 85% of the number of pups born throughout Britain. The total number of seals associated with these regularly surveyed sites is estimated by applying a population model to the estimates of pup production. Estimates of the total number of seals at other breeding colonies that are surveyed less frequently are then added in to give an estimate of the total British grey seal population. Further details are given in Annex II and Annex IV. Pup production The total number of pups born in 2001 at all annually surveyed colonies was estimated to be 36,920. A further 5,000 pups were likely to have been born at other scattered sites. Regional estimates were 2,938 in the Inner Hebrides, 12,325 in the Outer Hebrides, 17,523 in Orkney, and 4,134 at North Sea sites. Pup production and total population size estimates for the main colonies surveyed in 2001 Location 2001 pup Change in pup Change in pup Total 2001 production production production population (to from 2000- from 1997- nearest 1000) 2001 2001 Inner Hebrides 2,938 -8.8% -0.5% 9,000 Outer Hebrides 12,325 -8.0% +1.4% 38,000 Orkney 17,523 +9.6% +4.4% 54,000 Isle of May + Fast 2,253 -10.4% +3.3% 7,000 Castle All other colonies 3,500 11,000 Total (Scotland) 38,539 119,000 Donna Nook 634 +2.6% +14.5% 2,000 Farne Islands 1,247 +6.5% -1.7% 4,000 SW England & 1,500 5,000 Wales (last surveyed 1994) Total (England) 3,381 11,000 Total (UK) 41,920 0.0%* +2.8% 130,000 *Annual change in pup production calculated from annually monitored sites only Trends in pup production Between 1984 and 1996, estimates of the total number of pups born at regularly surveyed colonies increased year on year (Annex II, Figures 2 & 3). A small decline was observed in 1988 that was probably related to the effect of a phocine distemper epidemic that mainly affected common seals at that time. Following this event, estimated total pup production did not show any decline until 1997. It recovered again in 1998 then declined at all major breeding colonies in 1999. The greatest decline was at the Farne Islands, where pup counts are made by National Trust staff on the ground. That declines occurred at the Farne Islands and at other sites where pup production is monitored by aerial survey suggested that this was a general phenomenon and not related to differences in methods or 4 SCOS 02/2 survey conditions from previous years.